Asset Retirement Obligations and Accrued Environmental Costs (Asset Retirement Obligations and Accrued Environmental Costs) (Details) - USD ($) $ in Millions |
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|---|
| Asset Retirement Obligations and Accrued Environmental Costs [Abstract] | |||
| Asset retirement obligations | $ 5,926 | $ 5,573 | $ 6,206 |
| Accrued environmental costs | 187 | 180 | |
| Total asset retirement obligations and accrued environmental costs | 6,113 | 5,753 | |
| Asset retirement obligations and accrued environmental costs due within one year | (359) | (323) | |
| Long-term asset retirement obligations and accrued environmental costs | $ 5,754 | $ 5,430 |